TB, I would keep the garage the same size, the extra bit at the back would be a seperate room/outhouse. This could have an access door into the garage or one to the garden.
This gives you multiple options as it can then be insulated to a higher standard (potentialy in the future) and used for many more purposes than storage.
Or it could simply be a better built shed (did you loose a shed also?)
The shed was removed 3 or 4 years back, and now lives on (with fresh felt
) over at my little bro's.
Now he has a nice 3 berth garage, but still swamped by his neighbour - Mum - with her 4 berth, with a brick workshop out the back. Lucky mare.
Office style space is probably what I would make it *if* its financially viable to both me and my neighbour. We both need to do it, else its unworkable (or flat roof, which I do not want). This would add the most value, even though it would only ever be used to store junk while I live there.